Application of different isolation schemes for logic and embedded memory

ABSTRACT

The present invention facilitates semiconductor device fabrication by providing mechanisms for utilizing different isolation schemes within embedded memory and other logic portions of a device. The isolation mechanism of the embedded memory portion is improved relative to other portions of the device by increasing dopant concentrations or reducing the depth of the dopant profiles within well regions of the embedded memory array. As a result, smaller isolation spacing can be employed thereby permitting a more compact array. The isolation mechanism of the logic portion is relatively less than that of the embedded memory portion, which permits greater operational speed for the logic.

FIELD OF THE INVENTION

The present invention relates generally to the field of semiconductordevices, and more particularly, to different isolation schemes for logicand embedded memory in semiconductor devices.

BACKGROUND OF THE INVENTION

Electronic devices typically include a number of individual componentssuch as memory, logic, and the like. In the past, these individualcomponents have been formed on separate die or chips. These separatechips were packaged separately and attached to one or more circuitboards of the electronic device. The circuit board contained thenecessary interconnects to attain desired functionality from theindividual components. As a result, the electronic device as a wholeoperated according to the individual components formed andinterconnected via one or more circuit boards and electronicconnections.

One problem with utilizing individual components packaged separately isthat great/substantial reductions in die or component sizes do notalways yield the same reduction in component size due to the fact thatpackaging and interconnects do not generally reduce in proportion. Thus,desired scaling/shrinking, which is a continuing demand for electronicdevices, may not be obtained despite reduction in die sizes.

One potential solution is to combine multiple components onto a singledie. Thus, for example, logic can be combined with embedded memory on asingle die. The necessary interconnects between the logic and theembedded memory are formed within/on the die thereby reducing the needfor interconnects on a circuit board, separate packaging, heatsinks, andthe like. Additionally, performance gains can be achieved by reducingtransmission path lengths and the like between components.

However, some desired space savings can be lost by combining multiplecomponents onto a single die. Fabrication procedures employed formultiple components may not be as well suited as procedures employed forsingle, specific components. As a result, in some instances at least aportion of one or more components may be fabricated to a relativelylarger size than would otherwise be done.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basicunderstanding of one or more aspects of the invention. This summary isnot an extensive overview of the invention, and is neither intended toidentify key or critical elements of the invention, nor to delineate thescope thereof. Rather, the primary purpose of the summary is to presentsome concepts of the invention in a simplified form as a prelude to themore detailed description that is presented later.

The present invention facilitates semiconductor device fabrication byproviding mechanisms for utilizing different isolation schemes withinembedded memory and other logic portions of a device. The isolationperformance of the embedded memory portion is improved relative to otherportions of the device by increasing dopant concentration within wellregions therein. As a result, smaller (n+-p+) isolation spacing can beemployed thereby permitting a more compact design. The isolation in thelogic portion uses lower doping/concentration than that of the embeddedmemory portion, which permits lower capacitance and therefore greateroperational speed within the logic. Thus, reduced spacing is achievedwithin the memory portion without negatively impacting deviceperformance within the logic portions of the die.

A number of suitable methods are employed to achieve the differentisolation schemes. One method utilizes additional pattern levels toperform a supplemental isolation implant within the embedded memoryportion. Another uses pattern levels that are already utilized in theprocess flow to fabricate high-threshold-voltage transistors to alsoperform supplemental isolation implants within the embedded memoryportion. Yet another employs additional pattern levels to allow fordistinct isolation implants in the logic and memory portions, with theimplants in the memory portion being relatively shallower than those inthe logic.

To the accomplishment of the foregoing and related ends, the inventioncomprises the features hereinafter fully described and particularlypointed out in the claims. The following description and the annexeddrawings set forth in detail certain illustrative aspects andimplementations of the invention. These are indicative, however, of buta few of the various ways in which the principles of the invention maybe employed. Other objects, advantages and novel features of theinvention will become apparent from the following detailed descriptionof the invention when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a semiconductor device comprising embeddedmemory in accordance with an aspect of the present invention.

FIG. 2 is a diagram illustrating exemplary n+-p+ isolation spacing for asemiconductor device in accordance with an aspect of the presentinvention.

FIG. 3 is a flow diagram illustrating a method of fabricating asemiconductor device with a higher channel stop in accordance with anaspect of the present invention.

FIG. 4 is a plan view of a semiconductor device and associated resistpatterns in accordance with an aspect of the present invention.

FIG. 5 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 6 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 7 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 8 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 9 is a flow diagram illustrating a method of fabricating asemiconductor device with a higher channel stop utilizing existingpattern levels originally employed for threshold-adjust channel implantsin accordance with an aspect of the present invention.

FIG. 10 is a plan view of a semiconductor device and associated resistpatterns in accordance with an aspect of the present invention.

FIG. 11 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 12 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 13 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 14 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 15 is a flow diagram illustrating a method of fabricating asemiconductor device with a higher channel stop utilizing existingpattern levels employed for threshold-adjust pocket implants inaccordance with an aspect of the present invention.

FIG. 16 is a plan view of a semiconductor device and associated resistpatterns in accordance with an aspect of the present invention.

FIG. 17 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 18 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 19 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 20 is a cross sectional diagram illustrating a stage of fabricationof a semiconductor device in accordance with an aspect of the presentinvention.

FIG. 21 is a flow diagram illustrating a method of fabricating asemiconductor device, wherein isolation implants are shallower withinthe memory portion within the device in accordance with an aspect of thepresent invention.

FIG. 22 is a cross sectional diagram illustrating deep implants in acore logic portion of a semiconductor device in accordance with anaspect of the present invention.

FIG. 23 is a cross sectional diagram illustrating relatively shallowimplants in a memory portion of a semiconductor device in accordancewith an aspect of the present invention.

FIG. 24 is a cross sectional diagram illustrating deep implants in acore logic portion of a semiconductor device in accordance with anaspect of the present invention.

FIG. 25 is a cross sectional diagram illustrating relatively veryshallow implants in a memory portion of a semiconductor device inaccordance with an aspect of the present invention.

FIG. 26 is a plan view schematic diagram of memory cells with buttedcontacts to the relatively very shallow N-well.

FIG. 27 is a graph illustrating a dopant profile for an n-well within alogic region in accordance with an aspect of the present invention.

FIG. 28 is a graph illustrating a dopant profile for an p-well within alogic region in accordance with an aspect of the present invention.

FIG. 29 is a graph illustrating a dopant profile for an n-well within anembedded memory array in accordance with an aspect of the presentinvention.

FIG. 30 is a graph illustrating a dopant profile for a p-well within anembedded memory array in accordance with an aspect of the presentinvention.

FIG. 31 is a graph illustrating a shallow dopant profile for an n-wellwithin an embedded memory array in accordance with an aspect of thepresent invention.

FIG. 32 is a graph illustrating a shallow dopant profile for a p-wellwithin an embedded memory array in accordance with an aspect of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described with respect to theaccompanying drawings in which like numbered elements represent likeparts. The figures provided herewith and the accompanying description ofthe figures are merely provided for illustrative purposes. One ofordinary skill in the art should realize, based on the instantdescription, other implementations and methods for fabricating thedevices and structures illustrated in the figures and in the followingdescription.

The present invention provides systems and methods that can reducedimensions and area consumption of semiconductor devices by facilitatingtighter spacing for an embedded memory portion of a semiconductordevice. In conventional devices that include embedded memory, the sameisolation doping profiles are employed for the embedded memory and logicportions of the device, limiting the extent to which memory n+-p+isolation spacings (across well boundaries) can be reduced. However, theinventors of the present invention appreciate that often, embeddedmemory does not require the same speed of operation as logic and/or therequirement for small memory size is more important than memory speed.As a result, the embedded memory portion can therefore employ differentdoping profiles to achieve relatively tighter isolation spacing.Accordingly, the present invention employs different isolation dopingprofiles for the embedded memory portion that facilitates deviceshrinkage. The term isolation doping profile refers to those portions ofthe doping profile that affect the isolation performance and comprisesvaried concentrations throughout a depth of a well. Likewise, the termisolation implants refers to those implants that contribute to theseportions of the doping profile. In most cases, the isolation dopingprofile would be the deeper portions of the profile below the source anddrain and the implants contributing to these portions would beprincipally the channel-stop and well implants.

Beginning with FIG. 1, a block diagram of a semiconductor device 100comprising embedded memory in accordance with an aspect of the presentinvention is depicted. The device 100 presented and discussed is merelyexemplary of devices that can be fabricated in accordance with thepresent invention. The device 100 is formed within and/or on asemiconductor substrate.

The device 100 includes an embedded memory array 102, high thresholdvoltage logic 104, and logic 106 and is formed in/on a semiconductormaterial or wafer. It is appreciated that the present invention includesvariations in which the device 100 does not include high thresholdvoltage logic 104. Although not shown, the device 100 can include othercomponents, including other embedded memory arrays, which may differfrom the memory array 102 in memory type or in speed and sizerequirements. For example, these other memory arrays may be intended forhigh-speed operation and their size may be relatively less important.Unlike similar conventional devices, the embedded memory array 102 andthe logic 106 are formed with different isolation mechanisms in order toincrease density and decrease the overall size of the semiconductordevice 100. Generally, the memory array 102 employs an isolationmechanism comprising relatively narrower isolation regions betweenactive regions across well regions of differing type, and higher dopantconcentrations within the well regions, than the isolation mechanismemployed by the logic 106. The isolation mechanism of the memory array102 permits a greater density for transistors within the memory arraythan would otherwise be achieved by employing the isolation mechanismemployed for the logic 106.

Smaller n+-p+ isolation spacing requires more aggressive (e.g.,relatively higher dopant concentration and/or shallower) isolationdoping profiles. These profiles typically produce relatively higherjunction capacitance, which reduces operating speed. As a result, thereis a trade-off between how small the isolation spacing is and how fast acircuit using that isolation spacing may operate.

The logic 106 and the memory array 102 have differing junctioncapacitance requirements. Generally, the logic 106 is required tooperate at relatively high speeds, which necessitate relatively lowjunction capacitance. The memory array 102, on the other hand, may beable to tolerate higher junction capacitance. This may be, for example,because the memory array 102 is not required to operate at relativelyhigh speeds, or because the requirement for small memory cell size ismore important than that for speed. Thus, isolation schemes usingshallower or higher-concentration doping profiles, such as employed forthe memory array 102, increase the junction capacitance in the memoryarray. However, because the acceptable junction capacitance for thememory array 102 may be higher than that required for the logic 106, thememory array 102 can tolerate such aggressive doping profiles and stillperform acceptably. The high threshold-voltage logic 104, in thoseaspects of the invention where it is present, typically has lower speedrequirements than the logic 106, and can therefore tolerate highjunction capacitance similar to that of the memory array 102.

Conventionally, the same isolation implants where used for logic andembedded memory arrays. This resulted in either a relatively largermemory cell size to keep the logic capacitance low, or a relativelylarger logic junction capacitance to support a relatively smaller memorycell, or both.

Unlike conventional devices, the logic 106 and the memory array 102utilize different isolation implants as stated above. The logic 106employs less aggressive dopant profiles to achieve low junctioncapacitance and high speed at the expense of relatively large n+-p+isolation spacing, whereas the memory array 102 employs more aggressivedopant profiles in order to reduce the isolation spacing andreduce/conserve area. Some exemplary dopant profiles are shown in FIGS.27-32 and described infra.

The distinct isolation mechanisms employed for the logic 106 and thememory array 102 can be formed or fabricated in a number of suitableways. Shallow trench isolation (STI) regions of different widths can beformed by etching trenches to the differing widths andfilling/depositing with a dielectric such as oxide according to one ormore suitable fabrication procedures. The different resulting dopantconcentrations can be achieved by implanting dopants for the logic 106and the memory array 102 in separate procedures/processes and/or byperforming a first implant for the logic 106 and the memory array 102followed by a supplemental isolation/well implant for only the memoryarray 102. In those aspects of the invention where the high-thresholdvoltage logic 104 is present, n-well and/or p-well areas associated withthe high voltage threshold logic 104 and the memory array 102 areexposed for stand-alone and/or supplemental implants. The n-well region,p-well region, or both can receive stand-alone and/or supplementalimplants depending on the trade-off between junction capacitance andisolation spacing for each polarity. Finally, the memory well regions tobe exposed for stand-alone and/or supplemental isolation/well implantsmay be exposed using additional resist pattern levels or resist patternlevels already present in the process flow. Additional resist patternlevels are pattern levels that would not exist in the process flow ifisolation/well implants were the same in all regions of the chip. Resistpattern levels already present in the process flow are any patternlevels that would exist in the process flow even if isolation/wellimplants were the same in all regions of the chip.

FIG. 2 illustrates exemplary n+-p+ isolation spacing for a device inaccordance with an aspect of the present invention. This FIG. 2 isprovided for illustrative purposes and is not intended to limit thepresent invention to particular sizes, dimensions, configurations, andthe like. Generally, elements (e.g., transistors and the like) formedwithin/on a semiconductor device are at least partially isolated fromeach other by isolation regions. These regions prevent or mitigateeffects of one element or component from affecting another. FIG. 2 showsa common type of isolation region referred to as a shallow trenchisolation (STI) region. For a logic portion of the device, STI regionsare illustrated with a logic n+-p+ isolation spacing 202. Similarly, fora memory array portion, STI regions 208 are depicted with a memory n+-p+isolation spacing 204. From FIG. 2, it can be seen that the logicisolation spacing 202 is relatively larger than the memory isolationspacing 204. Actual values of n+-p+ isolation spacings depend on manyfactors, such as the year and technology node. However, exemplary valuesat some given time may be 300 nm for the logic and 200 nm for the memoryarray.

Returning now to FIG. 1, the different isolation spacing for the logic106 and the memory array 102 can be achieved by any number of suitabletechniques. A first technique is to employ additional pattern levels ormasks in order to form the isolation regions distinctly. Conventionally,the isolation regions were formed via a single set of pattern levelsthat forms substantially similar spaced isolation regions within logicand memory regions. Employing additional pattern levels facilitatesforming different isolation regions but can increase cost ofproduction/fabrication as a result of the added pattern levels. A secondtechnique is to employ existing pattern levels already used in thattechnology for other purposes (e.g., for high threshold voltagepatterns). The advantage of this technique is that additional patternlevels and processing steps can, at least partly, be avoided.

FIG. 3 is a flow diagram illustrating a method 300 of fabricating asemiconductor device with a higher channel-stop or well dose (distinctisolation mechanism) for a memory array portion of the device than alogic portion of the device by employing additional pattern levels inaccordance with an aspect of the present invention. The semiconductordevice includes an embedded memory portion and a logic portion. Themethod 300 is provided as an exemplary method in which to utilizedifferent isolation schemes for the embedded memory and the logicportions on the device in accordance with the present invention. Themethod 300 is further described with respect to FIGS. 4-9 so as tofurther illustrate the method 300. However, it is appreciated thatvariations in structure from FIGS. 4-9 are permitted in accordance withthe present invention.

FIG. 4 is a plan view of the device and additional resist patterns ofFIG. 3 in accordance with an aspect of the present invention. A top view401 of the device illustrates the embedded memory portion 404 and thelogic portion 406 (other areas of the device). A supplemental n-wellresist layer 402 and a supplemental p-well resist layer 403 are alsoshown. These layers are employed and described further below.

The method 300 begins at block 302 where a p-well implant is performedfor both the logic and embedded memory portions by selectivelyimplanting one or more p-type dopants (e.g., boron) at selected doses,angles, and energies. As a result, p-well regions are selectively formedwithin a semiconductor substrate with a selected/desired concentrationand depth profile. FIG. 5 is a cross sectional diagram that depicts thedevice at this stage of fabrication in accordance with an aspect of thepresent invention. Shallow trench isolation (STI) layers 510 within thelogic portion 406 and STI layers 512 within the embedded memory portion404 are already present prior to the p-well regions formation in thepresent example. A first patterned resist layer 514 is employed todefine p-well regions in the substrate, and one or more p-type implants516 are performed to form p-well regions 508 throughout the device inboth the logic portion 406 and the embedded memory portion 404. Theseimplants may include a relatively deep well implant, a shallowerchannel-stop implant, a still shallower punch-through implant, and astill shallower channel implant. Subsequent to the implant(s), the firstresist layer 514 is removed from the device.

Continuing at block 304,n-well areas are formed for both the logic andembedded memory regions by selectively implanting one or more n-typedopants (e.g., phosphorous or arsenic) at selected doses, angles, andenergies. FIG. 6 serves to illustrate the device at this stage offabrication in accordance with an aspect of the present invention. Asecond resist layer 618 is employed to selectively implant one or moren-type dopants 620 into the device forming n-well regions 622 in boththe logic portion 406 and the embedded memory portion 404. Theseimplants may include a relatively deep well implant, a shallowerchannel-stop implant, a still shallower punch-through implant, and astill shallower channel implant. The second resist layer 618 prevents ormitigates the n-type dopant 620 from entering the p-well regions 508.Also, the second resist layer 618 is removed from the device subsequentto the implant of block 304 of FIG. 3.

At block 306, one or more supplemental implants are performed for theembedded memory regions by selectively implanting one or more p-typedopants into p-well regions within the memory portion. FIG. 7 is a crosssectional diagram that illustrates the device at this stage offabrication in accordance with an aspect of the present invention. Here,one or more p-type dopants 724 are selectively implanted into p-wellregions 726 of the embedded memory portion 404 of the substrate. Thep-well resist layer 403 is employed to define the one or more regions726 for the implant. The implants may include a relatively deepsupplemental well implant or a shallower supplemental channel-stopimplant. The supplemental implants are performed with a dose and energyso as to achieve a desired dopant concentration profile in the p-wellregions 726. Exemplary concentrations with and without the supplementalimplants are shown in FIGS. 27-32 and described infra. The resist layer403 is removed after performing the implant.

One or more supplemental n-type dopants are implanted in the embeddedmemory regions at block 308 of FIG. 3. FIG. 8 is a cross sectionaldiagram that depicts the device at this stage of fabrication inaccordance with an aspect of the present invention. Here, one or moren-type dopants 828 are selectively implanted into n-well regions 830 ofthe embedded memory portion 404. The resist layer 402 is employed todefine the region 830 for the implant. Additionally, the implant(s) areperformed with a dose and energy so as to achieve a desired dopantconcentration profile in the n-well regions 830. Exemplaryconcentrations with and without the supplemental implants are shown inFIGS. 27-32 and described infra. The resist layer 402 is removed afterperforming the implant. It is appreciated that the present inventionincludes variations of this method 300 wherein only one of thesupplemental p-well and supplemental n-well implants is performed anddoes not require the blocks being performed in a specific order.Furthermore, the four blocks described supra 302, 304, 306, and 308 canbe performed in any suitable order.

Continuing at block 310, standard processing is performed on the device.The standard processing includes forming gate structures, spacers,contacts, metal interconnects and vias, packaging, and the like in orderto complete fabrication of the device.

Still referring to FIG. 8, note that a spacing 831 between activeregions in the well regions 726, 830 in the memory area 404 (as dictatedby the STI 512) is substantially smaller than a spacing 832 in the logicportion 406 of the device. The substantially reduced spacing 831 isenabled because the well regions 726, 830 are more heavily doped due tothe supplemental implants (blocks 306 and 308 of FIG. 3) therein.Accordingly, devices needing isolation from one another within thememory array portion 404 can be spaced closer together, therebyimproving packing density therein.

FIG. 9 is a flow diagram illustrating a method 900 of fabricating asemiconductor device with a higher channel-stop or well dose (distinctisolation mechanism) for a memory array of the device than a logicportion by employing existing pattern levels used for threshold-adjustchannel implants for high threshold-voltage transistors. The deviceincludes an embedded memory portion, a core logic portion, and possiblya high-threshold-voltage logic portion. The embedded memory arrayutilizes high-threshold-voltage transistors. The embedded memory arraymay utilize high-threshold-voltage transistors in order to improved cellstability. A high-threshold voltage logic portion that exist outside theembedded memory array is not required for the method 900.

The method 900 is provided as an exemplary method in which to utilizedifferent isolation schemes for the embedded memory and the core logicportions on the device without employing additional pattern levels orprocedures as is done with method 300 of FIG. 3. The method 900 performssupplemental isolation implants into the embedded memory after theresist patterns used for channel threshold-adjust implants forhigh-voltage transistors are formed and before they are removed, whicheliminates the need for additional pattern levels. The method 900 isalso described with respect to FIGS. 10-14 so as to further illustratethe method 900. However, it is appreciated that variations in structurefrom FIGS. 10-14 are contemplated and permitted in accordance with thepresent invention.

FIG. 10 is a plan view of the device of FIG. 9 and high thresholdvoltage resist layers in accordance with an aspect of the presentinvention. A top view 1001 of an exemplary device illustrates theembedded memory portion 1004, the core logic portion 1006, and the highthreshold voltage logic portion 1008. A high-Vt n-well resist layer 1002and a high-Vt p-well resist layer 1003 are also shown. These layers areemployed and described further below. The method 900 begins at block 902where p-well regions are formed for the core logic portion, highthreshold voltage logic portion and embedded memory portion of thedevice by selectively implanting one or more p-type dopants into thesubstrate with selected doses, energies, and angles. FIG. 11 is a crosssectional diagram that depicts the device at this stage of fabricationin accordance with an aspect of the present invention. Shallow trenchisolation (STI) regions 1114 within the core logic portion 1006, STIregions 1116 within the high threshold voltage logic portion, and STIregions 1118 within the embedded memory portion 1004 are already formedin this example. A first patterned resist layer 1120 is employed toselectively implant one or more p-type dopants 1122 into and formingp-well regions 1108,1110, and 1112, located respectively in the corelogic portion 1006, the high threshold voltage logic portion 1008, andthe embedded memory portion 1004. These implants may include arelatively deep well implant, a shallower channel-stop implant, a stillshallower punch-through implant, and a still shallower channel implant.Subsequent to the implants, the first resist layer 1120 is removed fromthe device.

Continuing at block 904, n-well areas are formed for the core logicportion, high threshold voltage logic portion and embedded memoryportion by selectively implanting one or more n-type dopants (e.g.,phosphorous or arsenic) at selected doses, angles, and energies. FIG. 12serves to illustrate the device at this stage of fabrication inaccordance with an aspect of the present invention. A second patternedresist layer 1230 is employed to selectively implant one or more n-typedopants 1232 into and forming n-well regions 1224, 1226, and 1228located respectively in the core logic portion 1006, the high thresholdvoltage logic portion 1008, and the embedded memory portion 1004. Theseimplants may include a relatively deep well implant, a shallowerchannel-stop implant, a still shallower punch-through implant, and astill shallower channel implant. The second resist layer 1230 preventsor mitigates the dopant 1232 from implanting into the p-well regions(1108, 1110, and 1112).

Exemplary concentrations with and without the supplemental implants areshown in FIGS. 27-32 and described infra.

At block 906, one or more supplemental isolation implants are performedinto the high-Vt and embedded memory p-well regions. FIG. 13 illustratesthe device at this stage of fabrication in accordance with an aspect ofthe present invention. As illustrated in FIG. 13, at this stage of theprocess, the high-Vt p-well resist layer 1003 is present and is used toselectively implant one or more p-type dopants in the high-Vt and memoryp-well regions in order to raise the threshold voltage of transistorssubsequently formed in these regions. In accordance with an aspect ofthe present invention, while this resist layer is still present, one ormore p-type dopants 1334 are now implanted into p-wells 1110 of thehigh-Vt logic portion 1008 and p-wells 1112 of the embedded memoryportion 1004 as supplemental isolation implants, thereby improvingisolation. Exemplary concentrations with and without the supplementalimplants are shown in FIGS. 27-32 and described infra. Unlike the method300 of FIG. 3, this method 900 does not require additional patternlevels because the supplemental implant is performed during thethreshold voltage raising process sequence.

Continuing at block 908, one or more supplemental isolation implants areperformed into the high-Vt and embedded memory n-well regions. FIG. 14serves to illustrate the device at this stage of fabrication inaccordance with an aspect of the present invention. As illustrated inFIG. 14, at this stage of the process, a high VT n-well resist layer1002 is present. This layer is typically employed to selectively implantone or more n-type dopants into the high-Vt and memory n-well regions inorder to raise the threshold voltage of transistors subsequently formedin these regions. In accordance with an aspect of the present invention,while this resist layer is still present, one or more p-type dopants1436 are now implanted into n-wells 1226 of the high-Vt logic portion1008, and into n-wells 1228 of the embedded memory portion 1004 assupplemental isolation implants, thereby improving isolation. Again,unlike the method 300 of FIG. 3, this method 900 does not requireadditional pattern levels because the supplemental implant is performedduring the threshold voltage raising process sequence. Furthermore, itis appreciated that the present invention includes suitable variationsof this method 900 wherein only some of the transistors in the memoryarray are high-threshold-voltage transistors, and/or wherein only one ofthe supplemental p-well and supplemental n-well implants is performed.Additionally, it is appreciated that the method 900 can be performed inany suitable order and can include additional processing steps.

Standard processing is performed on the device at block 910 in order tocomplete fabrication of the device. The standard processing includesforming active regions, gate structures, spacers, contacts, metalinterconnects and vias packaging, and the like in order to completefabrication of the device.

Note that, for FIG. 14, a spacing of the STI regions 1118 for the memoryportion 1004 is smaller than a spacing of the STI regions 1114 for thecore logic portion 1006. The reduced spacing is permitted because thewell regions 1112 and 1228 are more heavily doped due to thesupplemental implants performed during the high threshold voltageimplants. Accordingly, the packing density of the memory array 1004 canbe improved. Additionally, note the reduced spacing is obtained withoutperforming extra patterning operations, as is the case with the method300 of FIG. 3.

FIG. 15 is a flow diagram illustrating a method 1500 of fabricating asemiconductor device with a higher channel-stop or well dose for amemory array of the device by employing pattern levels already used forhigh threshold voltage pocket implants subsequent to gate formation. Thedevice includes an embedded memory portion, a core logic portion, and ahigh-threshold-voltage logic portion. It is appreciated that, inalternate aspects of the invention, the high-threshold-voltage logicportion can be absent from the device. The embedded memory arrayutilizes at least some high-threshold-voltage transistors. However, themethod 1500 does not require that a high-threshold voltage logic portionexist outside the memory array. The method 1500 is provided as anexemplary method in which to utilize different isolation schemes for theembedded memory and the core logic portions on the device withoutemploying additional pattern levels or procedures. The method 1500performs supplemental isolation implants into the embedded memory duringthe same process steps employed in forming the high threshold voltagetransistors via pocket implants. The method 1500 is also described withrespect to FIGS. 16-20 so as to further illustrate the method 1500.However, it is appreciated that variations in structure from FIGS. 16-20are permitted in accordance with the present invention.

A pocket implant, also referred to as a halo implant, is a techniqueemployed to reduce sensitivity of the performance of a transistor tocharacteristics such as gate length. Generally, the pocket implantsurrounds source and drain regions and thus reduces punch-throughleakage. The pocket implant is typically defined by its peakconcentration depth and the amount of gate underlap controlled by animplant angle.

FIG. 16 is a plan view of the device of FIG. 15 and high thresholdvoltage pocket implant resist layers in accordance with an aspect of thepresent invention. A top view 1601 of the device illustrates theembedded memory portion 1604, the core logic portion 1606, and the highthreshold voltage logic portion 1608. A high-Vt n-well resist layer 1602and a high-Vt p-well resist layer 1603 employable in thresholdadjustment pocket implants are also shown. These layers are employed anddescribed further below.

The method 1500 begins at block 1502 where p-wells are formed for thecore logic portion, high threshold voltage logic portion and embeddedmemory portion. FIG. 17 is a cross sectional diagram that depicts thedevice at this stage of fabrication in accordance with an aspect of thepresent invention. Shallow trench isolation (STI) regions 1714 withinthe core logic portion 1606, STI regions 1716 within the high thresholdvoltage logic portion, and STI regions 1718 within the embedded memoryportion 1604 are already formed. A first patterned resist layer 1720 isemployed to selectively implant one or more p-type dopants 1722 to formp-well regions 1708, 1710, and 1712, located respectively in the corelogic portion 1606, the high threshold voltage logic portion 1608, andthe embedded memory portion 1604. These implants may include arelatively deep well implant, a shallower channel-stop implant, a stillshallower punch-through implant, and a still shallower channel implant.Subsequent to the implant, the first resist layer 1720 is removed fromthe device.

Continuing at block 1504, n-wells are formed for the core logic portion,high threshold voltage logic portion and embedded memory portion. FIG.18 serves to illustrate the device at this stage of fabrication inaccordance with an aspect of the present invention. A second patternedresist layer 1830 is employed to selectively implant one or more n-typedopants 1832 to and form n-well regions 1824, 1826, and 1828 locatedrespectively in the core logic portion 1606, the high threshold voltagelogic portion 1608, and the embedded memory portion 1604. These implantsmay include a relatively deep well implant, a shallower channel-stopimplant, a still shallower punch-through implant, and a still shallowerchannel implant. The second resist layer 1830 prevents or mitigates thedopant 1832 from implanting into the p-well regions (1708, 1710, and1712). Subsequent to the implant, the second resist layer 1830 isremoved from the device.

Gate structures are formed within the various n-well and p-well regionsat block 1506. A series of semiconductor fabrication processes includingdepositing and patterning are employed to form the gate structure.

At block 1508, one or more supplemental isolation implants are performedinto the high-Vt and embedded memory p-well regions. FIG. 19 illustratesthe device at this stage of fabrication in accordance with an aspect ofthe present invention. As illustrated in FIG. 19, at this stage of theprocess, a high-Vt p-well resist layer 1603 is present. This layer istypically used to selectively implant one or more p-type dopants in thehigh-Vt and memory p-well regions as pocket implants in order to raisethe threshold voltage of transistors in these regions. In accordancewith an aspect of the present invention, while this resist layer isstill present, one or more p-type dopants 1936 are now implanted intop-wells 1710 of the high-Vt logic portion 1608 and p-wells 1712 of theembedded memory portion 1604 as supplemental isolation implants, therebyimproving isolation.

Continuing at block 1510, one or more supplemental isolation implantsare performed into the high-Vt and embedded memory n-well regions. FIG.20 serves to illustrate the device at this stage of fabrication inaccordance with an aspect of the present invention. As illustrated inFIG. 20, at this stage of the process, a high VT n-well resist layer1602 is present. This layer is typically employed to selectively implantone or more n-type dopants into the high-Vt and memory n-well regions aspocket implants in order to raise the threshold voltage of transistorsin these regions. In accordance with an aspect of the present invention,while this resist layer is still present, one or more p-type dopants2040 are now implanted into n-wells 1826 of the high-Vt logic portion1608, and into n-wells 1828 of the embedded memory portion 1604 assupplemental isolation implants, thereby improving isolation. Again,unlike the method 300 of FIG. 3, this method 1500 does not requireadditional pattern levels because the supplemental implant is performedduring the threshold voltage raising process sequence. Furthermore, itis appreciated that the present invention includes variations of thismethod 1500 wherein only one of the supplemental p-well and supplementaln-well implants is performed, and wherein the blocks 1502 and 1504 areperformed in any suitable order, and the two blocks 1508 and 1510 areperformed in any suitable order. Standard processing is performed on thedevice at block 1512 in order to complete fabrication of the device. Thestandard processing includes forming active regions, gate structures,spacers, contacts, metal interconnects and vias, packaging, and the likein order to complete fabrication of the device.

Turning now to FIG. 21, a flow diagram illustrating a method 2100 offabricating a semiconductor device wherein well/isolation implants areshallower within a memory portion of the device than within a core logicportion of the device. The shallower implants can yield improvedisolation and tighter n+-p+ spacing for the memory portion of the deviceby making the isolation performance more immune to misalignment.

As described previously, n-well and p-well regions are typicallyseparated in semiconductor devices by shallow trench isolation (STI)regions. The bottoms of these STI regions are generally narrow. As aresult, if a deep isolation/well implant is misaligned by even arelatively small amount, the implant will cross over into semiconductormaterial on an opposite side of the STI region, thereby degradingisolation. However, if the isolation/well implant is relatively shallow,relatively larger misalignments can occur without substantial isolationdegradation due to the wider extent of the STI region at the shallowerdepth. A drawback of the shallow well/isolation implant is that itincreases junction capacitance. However, this increase in junctioncapacitance can be acceptable for the memory regions of devices.

The method 2100 begins at block 2102 wherein one or more implants areperformed to form a plurality of n-wells to a first depth in the corelogic portion of the device. These implants may include a relativelydeep well implant, a shallower channel-stop implant, a still shallowerpunch-through implant, and a still shallower channel implant. The firstdepth is determined primarily by the deeper implants, including the welland/or channel-stop implants. A set of doses and energies are selectedand utilized to achieve the desired depth and desired concentrationprofile. Then, one or more implants are performed to form a plurality ofp-wells to a second depth in the core logic portion of the device. Thesecond depth can be comparable to the first depth, but is notnecessarily so. For the memory portion of the device, one or moreimplants are performed at block 2106 to form a plurality of n-wells to athird depth in the memory portion.

Continuing, a p-well implant is performed at block 2108 to a fourthdepth in the memory portion. The order and number of resist layers andmasks employed to perform the above blocks can vary and still be inaccordance with the present invention.

At block 2110, standard processing is performed on the semiconductordevice in order to complete fabrication of the device. The standardprocessing includes forming active regions, gate structures, spacers,contacts, metal interconnects and vias, packaging, and the like in orderto complete fabrication of the device.

FIGS. 22-26 presented below serve to further illustrate the method 2100of FIG. 21 by depicting examples of devices fabricated by the method2100 and variations thereof. FIG. 22 is a cross sectional diagramillustrating deep implants in a core logic portion of a semiconductordevice 2200 in accordance with an aspect of the present invention. Thedevice 2200 is depicted with an n-well region 2202, a p-well region 2204and an STI region 2206. The n-well region 2202 and the p-well region2204 have a greater depth than that of the STI region 2206. As a result,misalignment in performing the n-well and/or p-well implants can resultin degrading isolation of the respective regions. FIG. 23 is anothercross sectional diagram illustrating shallow implants in the memoryportion of a semiconductor device 2300 in accordance with an aspect ofthe present invention. The device 2300 includes a p-well region 2302, ann-well region 2304, and a STI region 2306. In this example, the p-wellregion 2302 and the n-well region 2304 are relatively shallower than theregions in FIG. 22. As a result, relatively larger implant misalignments(e.g., due to poor resist alignment) can occur without impactingisolation of the respective regions.

FIG. 24 is a cross sectional diagram illustrating deep implants in acore logic portion of a semiconductor device 2400 in accordance with anaspect of the present invention. The device 2400 is depicted with ann-well region 2402, a p-well region 2404 and an STI region 2406. Then-well region 2402 and the p-well region 2204 have a greater depth thanthat of the STI region 2406. FIG. 25 is another cross sectional diagramillustrating very shallow implants in the memory portion of asemiconductor device 2500 in accordance with an aspect of the presentinvention. The device 2500 also includes a p-well region 2502, an n-wellregion 2504, and a STI region 2506. In contrast to the regions of FIG.24, the p-well region 2502 and the n-well region 2504 do not have agreater depth that the STI region 2506, in this example. In fact, thep-well region 2502 and the n-well region 2504 have a depth such thatthey are adjacent to a relatively thick portion of the STI region 2506.As a result, relatively much larger implant misalignments can occurwithout impacting isolation of the respective regions.

One potential problem with shallow implant/well regions described aboveis that different active regions that would have been located within asingle shared deep well may no longer share a common well, each havingits own local well instead. For such cases, it may be necessary toconnect each local well to the desired potential using a butted contact.FIG. 26 is a diagram illustrating an example of a suitable topology 2600for a memory portion of a device in accordance with an aspect of thepresent invention. The topology 2600 includes active regions 2602,polysilicon layers 2604, n-well pattern 2606 and butted contacts 2608.Respective active regions 2602 are shown containing butted contacts2608, which connect to the underlying local n-wells.

It is appreciated that other suitable arrangements and topologies can beemployed in be in accordance with the present invention.

While, for purposes of simplicity of explanation, the methodologiesdescribed supra are depicted and described as executing serially, it isto be understood and appreciated that the present invention is notlimited by the illustrated order, as some aspects could, in accordancewith the present invention, occur in different orders and/orconcurrently with other aspects from that depicted and described herein.Moreover, not all illustrated features may be required to implement amethodology in accordance with an aspect the present invention.

FIGS. 27-32, discussed infra, are provided to illustrate exemplarysuitable dopant profiles that can be employed with the methodologiesdescribed supra. It is noted that other suitable dopant profiles can beemployed in accordance with the present invention. Such dopant profilescan be employed for a device that comprises at least a logic portion andan embedded memory portion, as described previously.

Beginning with FIG. 27, a graph illustrating a dopant profile for ann-well in a logic region in accordance with an aspect of the presentinvention is shown. An x-axis depicts depth form a well surface and ay-axis depicts dopant concentration. It can be seen that the dopantconcentration varies throughout the depth. FIG. 28 is a graphillustrating a dopant profile for a p-well within a logic region inaccordance with an aspect of the present invention. Again, an x-axisdepicts depth form a well surface and a y-axis depicts dopantconcentration. It can be seen that the dopant concentration also variesthroughout the depth.

FIG. 29 is a graph illustrating a dopant profile for for an n-wellwithin an embedded memory array in accordance with an aspect of thepresent invention. An x-axis depicts depth form a well surface and ay-axis depicts dopant concentration. Compared with the n-well within thelogic region, the n-well within the embedded memory has a relativelyhigher concentration. Turning to FIG. 30, a graph illustrating a dopantprofile for for a p-well within an embedded memory array in accordancewith an aspect of the present invention is shown. An x-axis depictsdepth form a well surface and a y-axis depicts dopant concentration.Compared with the p-well within the logic region, the p-well within theembedded memory has a relatively higher concentration. The higher dopantconcentrations shown in the embedded memory array result in a higherjunction capacitance for those regions. However, the relatively higherdopant concentrations permit tighter isolation spacing within theembedded memory array.

FIG. 31 is a graph illustrating a shallow dopant profile for for ann-well within an embedded memory array in accordance with an aspect ofthe present invention. An x-axis depicts depth form a well surface and ay-axis depicts dopant concentration. Compared with the n-well within thelogic region, the n-well within the embedded memory has a relativelyhigher concentration and is substantially shallower. Turning to FIG. 32,a graph illustrating a shallow dopant profile for for a p-well within anembedded memory array in accordance with an aspect of the presentinvention is shown. An x-axis depicts depth form a well surface and ay-axis depicts dopant concentration. Compared with the p-well within thelogic region, the p-well within the embedded memory has a relativelyhigher concentration and is also substantially shallower. The higherdopant concentrations shown in the embedded memory array result in ahigher junction capacitance for those regions. However, the relativelyhigher dopant concentrations permit tighter spacing within the embeddedmemory array.

Although the invention has been shown and described with respect to acertain aspect or various aspects, it is obvious that equivalentalterations and modifications will occur to others skilled in the artupon the reading and understanding of this specification and the annexeddrawings. In particular regard to the various functions performed by theabove described components (assemblies, devices, circuits, etc.), theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (i.e., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary embodiments of theinvention. In addition, while a particular feature of the invention mayhave been disclosed with respect to only one of several aspects of theinvention, such feature may be combined with one or more other featuresof the other aspects as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the term“includes” is used in either the detailed description or the claims,such term is intended to be inclusive in a manner similar to the term“comprising.”

1-25. (canceled)
 26. A semiconductor device comprising: a core logiccomprising a plurality of PMOS transistors formed in n-wells and NMOStransistors formed in p-wells, wherein adjacent MOS transistors areseparated across well boundaries by a shallow trench isolation regionhaving a first width an embedded memory array comprising a plurality ofPMOS transistors formed in n-wells and NMOS transistors formed inp-wells, wherein adjacent MOS transistors are separated are separatedacross well boundaries by a shallow trench isolation region having asecond width that is less than the first width, and wherein dopantconcentration of the n-wells and p-wells of the embedded memory aregreater than a dopant concentration of the n-wells and p-wells of thecore logic.
 27. The semiconductor device of claim 26, wherein the dopantconcentration of the n-wells in the core logic at a depth of 350 nm is8×10¹⁷ cm³ and the dopant concentration of the n-wells in the embeddedmemory array at a depth of 350 nm is 1.6×10¹⁸ cm³.
 28. The semiconductordevice of claim 26, wherein the MOS transistors of the embedded memoryarray have a relatively higher junction capacitance than the MOStransistors of the core logic.